Methods and compositions for enhancing processability and charge transport of polymer semiconductors and devices made therefrom

ABSTRACT

Methods of making solid-state semiconducting films. The methods include forming a mixture by mixing at least two monomers in a pre-determined proportion such that at least one of the at least two monomers contains at least one non-conjugation spacer. Polymerization of the mixture is achieved by reacting the monomers with one another resulting in a solid state polymer which is then purified. The purified solid state polymer is dissolved in an organic solvent to form a homogenous solution which is then deposited onto a substrate, forming a solid-state semiconducting film by evaporating the solvent. Alternatively, the purified solid state polymer is deposited onto a substrate and heated to form a liquid melt, and cooling the liquid melt results in a solid state semiconducting thin film. Also, films comprising a semiconducting polymer composition containing a minimum of one non-conjugation spacer and devices comprising such films.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. patent application is a divisional application ofco-pending U.S. patent application Ser. No. 15/045,953 filed Feb. 17,2016, which claims the priority benefit of U.S. Provisional PatentApplication Ser. No. 62/117,624 filed Feb. 18, 2015. The contents ofthese prior applications are hereby incorporated by reference in theirentirety into the present disclosure.

TECHNICAL FIELD

The present disclosure generally relates to methods and compositions forenhancing processability and charge transport of polymer semiconductors.

BACKGROUND

This section introduces aspects that may help facilitate a betterunderstanding of the disclosure. Accordingly, these statements are to beread in this light and are not to be understood as admissions about whatis or is not prior art.

Conjugated polymers are promising optoelectronic materials fornext-generation flexible and printed electronics. Conjugated polymersare a class of polymers with delocalized π-orbitals along the polymerbackbone. Extensive efforts have been put into the design and synthesisof conjugated polymers. A plethora of knowledge about how to rationallycontrol their optical, electronic, and redox properties has beenrealized in the development of numerous conjugated polymers. Incontrast, partially-conjugated semiconducting polymers withintentionally-placed, non-conjugated flexible linkages that allowconformation freedom along the polymer backbones have received littleattention. There are two primary reasons. First, flexible linkagescreate high degrees of conformational and energetic disorder in polymerchains. Second, conjugation-break spacers (CBSs) disrupt the extendedπ-electron delocalization along polymer backbones. Conjugation-breakspacers, also called non-conjugated spacers or non-conjugation spacersor non-conjugal spacers, are chemical groups that do not presentpi-conjugation along the polymer backbone and connect two conjugatedmoieties through covalent bonds. In principle, both factors can have anegative influence on electronic properties, particularly for chargetransport. On the other hand, high performance conjugated polymers areoften plagued with poor solution-processability, a leading factor forbatch-to-batch variations in both polymer synthesis and devicefabrication. This limits applications of conjugated polymers in largescale flexible electronics. Conventionally, tuningsolution-processability of polymers in organic solvents can be achievedby changing the size and shape of flexible solubilizing chains attachedto polymer backbones. However, the modulation of polymersolution-processability and electronic performance turns out to benontrivial as the factors that determine processability and electronicproperties are incompatible. It should be noted thatsolution-processability is a term used to describe the desirablecharacteristics of the solution, namely adequate solubility of thepolymer in this solvent, ability to make the solution as homogeneous aspossible in terms the polymer concentration, and the ability of thesolution to lend itself to depositing methods that provide uniformthickness and physical properties for films made from the solution.

Currently chlorinated solvents are utilized as solvents for polymersemiconductor materials for solution processing. These solvents aretoxic. Further the existing polymer semiconductors do not lendthemselves to melt-processing. Further, the existing polymersemiconductors do not lend themselves extrusion and laminationprocessing.

For the forgoing reasons, there exists a need for environmentallyfriendly approaches that can be applied to conjugated polymers toenhance their solution-processability as well as lending other types ofprocessability for the conjugated polymers making them into usefulpolymer semiconductors for electronic and optoelectronic applications.Further there is need for melt processable polymers and polymers thatlend themselves to extrusion and lamination processing.

SUMMARY

A method of making solid-state semiconducting films using asemiconducting polymer with enhanced solution processability isdisclosed. The method includes forming a mixture by mixing at least twomonomers in a pre-determined proportion, wherein at least one of the atleast two monomers contains at least one non-conjugation spacer;achieving polymerization of the mixture by reacting the at least twomonomers with one another resulting in a solid state polymer; purifyingthe solid state polymer resulting in a quantity of purified solid statepolymer; dissolving the quantity of the purified solid state polymer inan organic solvent to form a homogenous solution; depositing thehomogenous solution onto a substrate; and evaporating the solvent toform a solid-state semiconducting film.

A semiconducting polymer composition is disclosed. The compositionincludes comprising at least two monomers in a pre-determinedproportion, wherein at least one of the at least two monomers containsat least one non-conjugation spacer.

A method of making a solid state semiconducting films using asemiconducting polymer with melt processability is disclosed. The methodincludes mixing at least two monomers in a pre-determined proportion,wherein at least one of the two monomers contains at least onenon-conjugation spacer, to form a mixture; achieving polymerization ofthe mixture by reacting the at least three monomers with one anotherresulting in a solid state polymer; purifying the solid state polymerresulting in a quantity purified solid state polymer; depositing thepurified solid state polymer onto a substrate; heating the depositedpurified solid state polymer to form a liquid melt; and cooling theliquid melt to result in a solid state semiconducting thin film.

Also disclosed are devices containing films made from a semiconductingpolymer composition comprising at least two monomers in a pre-determinedproportion, wherein at least one of the at least two monomers containsat least one non-conjugation spacer.

BRIEF DESCRIPTION OF DRAWINGS

While some of the figures shown herein may have been generated fromscaled drawings or from photographs that are scalable, it is understoodthat such relative scaling within a figure are by way of example, andare not to be construed as limiting.

FIG. 1 shows UV-Vis-NIR spectra of DPP-100, DPP-70, DPP-50, DPP-30 andDPP-0 in solutions and as thin films.

FIG. 2A shows transfer characteristic of spin coated DPP-30 OFETs.

FIG. 2B shows Output characteristic of spin coated DPP-30 OFETs.

FIG. 3 shows the correlation between the mobility and the conjugationbreak spacer ratio obtained from the study on five polymers, namely,DPP-100, DPP-70, DPP-50, DPP-30 and DPP-0.

FIG. 4 shows transfer characteristic of melt processed DPP-70 OFETs.

FIG. 5 shows transfer characteristic of melt processed DPP-100 OFETs.

FIG. 6A is an AFM images of a spin coated DPP-100 film.

FIG. 6B is an AFM images of a melt processed DPP-100 film.

FIG. 6C is a GIXRD pattern for spin coated DPP-100 film.

FIG. 6D is a GIXRD pattern for melt processed DPP-100 film

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of thedisclosure is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the disclosure as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe disclosure relates.

In this disclosure, we report a novel strategy to address the problem ofthin film processing through molecular design. The strategy is tointroduce flexible CBSs into conjugated backbones. As mentioned earlier,conjugation-break spacers are chemical groups that do not presentpi-conjugation along the polymer backbone and connect two conjugatedmoieties through covalent bonds. In this disclosure conjugation-breakspacers are also referred to as called non-conjugated spacers ornon-conjugation spacers or non-conjugal spacers. Thus in thisdisclosure, the terms “conjugation-break spacers”, “non-conjugatedspacers”, “non-conjugation spacers”, and “non-conjugal spacers are usedinterchangeably and are considered synonymous. As will be demonstrated,this strategy not only provides a facile approach to modulatesolution-processability of the polymers, but it also unexpectedly offersa promising strategy to prepare melt-processable semiconductingpolymers. The former would make solution-processing more controllable.The latter could potentially eliminate the need for toxic organicsolvents for thin-film formation, which would have a positive impact onboth economic and environmental aspects. Understanding charge transportin disordered polymer films is a grand challenge in the field, as itplays a crucial role in next-generation semiconducting polymer designsand processes. This approach also provides a new platform forfundamental studies on charge transport from a different perspective.

Diketopyrrolopyrrole (DPP)-based semiconducting polymers have beenextensively investigated for their charge transport properties. Instudies leading to this disclosure, thediketopyrrolopyrrole-quaterthiophene copolymer was chosen as parentpolymer, and a propyl unit as a flexible CBS. The synthetic route forthe DPP polymers is shown in Scheme 1., shown below:

Pd₂(dba)₃ is tris(dibenzylideneacetone)dipalladium(0). P(o-tyl)3 istri(o-tolyl)phosphine. MW means microwave. The physical characterizationdata of the monomers and polymers of the scheme 1 are summarized inTable 1 below.

TABLE 1 Physical Properties of DPP polymers. T_(d) ^(b) T_(m) ^(c)λ_(max) ^(abs) (nm) λ_(onset) ^(abs) (nm) E_(g) ^(opt) _(f) Energylevels (eV) M_(n)(kDa)/PDI^(a) ° C. ° C. Solution^(d) Film^(e) Film^(e)(eV) E_(HOMO) ^(g) E_(LUMO) ^(h) DPP-0 30.7/3.61 400 — 740, 811 725, 789937 1.32 −4.97 −3.65 DPP-30 23.0/3.24 400 — 729 708 925 1.34 −5.01 −3.67DPP-50 19.5/2.60 399 — 699 687 915 1.36 −5.08 −3.72 DPP-70 16.9/2.20 395270, 180 645 654 907 1.37 −5.09 −3.72 DPP-100 12.5/1.98 390 180 594, 638595, 637 887 1.40 −5.13 −3.73 ^(a)Trichlorobenzene as the eluent at 180°C. ^(b)Decomposition temperature. ^(c)Melting temperature. ^(d)Indichlorobenzene solution. ^(e)Spin-coated films on glass substrates,annealed at 150° C. ^(f)Calculated from the onset absorptionE_(g) ^(opt)= 1240/λ_(onset) ^(abs) (nm). ^(g)Obtained from UPS. ^(h)Calculatedusing the equation E_(LUMO) = E_(HOMO) + E_(g) ^(opt).In Table 1 above, M_(n) is the number average molecular weight. kDa iskilodalton. PDI is polydispersity index. Td is decomposition temperatureand T_(m) is melting temperature. λ_(max) ^(abs) is the wavelength atmaximum absorption and λ_(onset) ^(abs) is the onset absorptionwavelength. E_(g) ^(opt) is the energy band gap calculated from opticalmeasurement. HOMO stands for the highest occupied molecular orbital andLUMO stands for the lowest unoccupied molecular orbital.

In the studies leading to this disclosure, ratio of the CBS is variedfrom 100%, 70%, 50%, 30% to 0%, namely from being fully flexible(DPP-100) to being fully rigid (DPP-0). The incorporation of propyllinkage was confirmed by monitoring the ratio between the number ofprotons in the CH₂ next to thiophene ring (chemical shift of ˜2.9 ppm)and the number of protons the CH₂ unit next to nitrogen atom (chemicalshift ˜4.0 ppm) in a nuclear magnetic resonance (NMR) study. UV-Vis-NIRspectra of DPP-100, DPP-70, DPP-50, DPP-30 and DPP-0 in solutions (dot)and as thin films (solid) are shown in FIG. 1. It is clear that thepresence of CBS breaks the n-conjugation along the polymer backbone,thus making the spectra blue-shifting.

The number-average molar mass and polydispersity were evaluated by hightemperature gel permeation chromatography (GPC) using trichlorobenzeneas the eluent at 180° C. and polystyrene for calibration. Thenumber-average molecular weights are 30.7, 23.0, 19.5, 16.9, and 12.5kDa for DPP-100, DPP-70, DPP-50, DPP-30 and DPP-0, with thepolydispersities of 3.61, 3.24, 2.60, 2.20, and 1.98, respectively. Thedifference in molecular weights for this set of polymers can beexplained by the degree of deviation from the random-coil model, whichis the basis for the universal calibration in the GPC measurement. Theless CBSs the polymers contain, the more we expect a deviation from therandom-coil model for the polymers.

The thermal stability for DPP polymers was evaluated by thermalgravimetric analysis (TGA). The decomposition temperatures are in therange of 390-400° C. Based on the weight loss information, it isbelieved that the decomposition starts from the loss of alkyl chains onthe nitrogen atoms. Differential scanning calorimetry (DSC) analysis wascarried out to obtain phase transition information. No noticeablethermal transition is observed in the range from 100 to 350° C. forDPP-0, 30 and 50, while DPP-70 and DPP-100 exhibit melting transitionsaround 270° C. and 180° C., respectively. The melting transitions ofDPP-70 and DPP-100 are not reversible even with a scanning rate as lowas 1° C./min. Upon heating and cooling on a hotplate, the polymersexhibit a reversible phenomenon of liquidation and solidification.

The solution and solid-state UV-Vis-NIR spectra of DPP polymers revealthe impact of propyl CBS on the optical properties, as summarized inTable 1. Referring to FIG. 1, a bathochromic (moving towards longerwavelength) shift is observed in both dichlorobenzene solutions andthin-films for this set of polymers (FIG. 1), due to the extension ofconjugation along the polymer backbone from DPP-100 to DPP-0. Fromsolution to thin film, DPP-0, DPP-30 and DPP-50 exhibit a clearhypochromic shift, whereas DPP-70 and DPP-100 show a limitedbathochromic shift with an obvious spectral broadening. It is noted thata broad absorption emerges around 800 nm in the DPP-100 thin film,indicating the formation of strong excitonic interactions and theformation of π-stacks. The HOMO energy levels of the polymers are in therange of −4.97 and −5.13 eV, estimated by ultraviolet photoemissionspectroscopy (UPS) and shown in Table 1. The difference in the HOMOlevels for DPP-0 and DPP-100 is about 0.16 eV. And the difference iseven smaller for the LUMO energy levels, only about 0.08 eV. It suggeststhat the LUMO level is more localized in a good agreement with thetheoretical calculation.

The introduction of CBSs into conjugated backbones improves polymersolution-processability as a result of disrupting of backbone rigidityand inducing higher conformational freedom in solution. Indeed, thesolubilities of these polymers in common organic solvents progressivelyincrease with the percentage of CBSs. For instance, DPP-30 exhibits muchimproved solubility in dichlorobenzene about ˜10 mg/mL, in comparisonwith that of DPP-0 (˜3 mg/mL). Fully flexible DPP-100 shows solubilitygreater than 50 mg/mL under the same conditions. On the other hand, itis understood that the gain in solubility will be accompanied by theloss in charge transport performance, because the presence of CBSsdisrupts the efficient intrachain charge transport pathway.

To investigate the influence of CBSs on the charge transport propertiesof these polymers, bottom-gate, bottom-contact organic field-effecttransistors (OFETs) were fabricated with silicon wafers as the back gateelectrode, a 300 nm thermally oxidized SiO₂ layer as the gatedielectric, and pre-patterned gold electrodes as the source/drain.Passivation of the SiO₂ layer was achieved by treating its surface withoctadecyltrichlorosilane (OTS). All mobility values reported here wereextracted from the electrical characteristics to ensure a fairassessment. Spin coated, drop-cast and melt-processed OFETs werefabricated and optimized. The device characteristics are summarized inTable 2 below.

TABLE 2 Field-effect performance characteristics of OFETs fabricated bydifferent processing methods. Spin coating Drop casting Melt processingμ_(max) μ_(ave) μ_(max) μ_(ave) μ_(max) μ_(ave) cm²/Vs cm²/Vs V_(Th) VI_(on)/I_(off) cm²/Vs cm²/Vs V_(Th) V I_(on)/I_(off) cm²/Vs cm²/VsV_(Th) V I_(on)/I_(off) DPP-0 4.27 3.52 −4.9 ~10⁶ 4.85 4.28 −4.3 ~10⁶ —— — — DPP-30 1.43 0.91 −4.3 ~10⁶ 1.44 1.05 −4.6 ~10⁶ — — — — DPP-50 0.440.27 −5.5 ~10⁵ 0.46 0.19 −6.1 ~10⁵ — — — — DPP-70 0.091 0.065 −7.9 ~10⁵0.095 0.069 −7.4 ~10⁵ 0.30 0.21 −4.3 ~10⁵ DPP-100 0.026 0.014 −9.2 ~10⁴0.027 0.016 −8.6 ~10⁵ 0.045 0.032 −4.5 ~10⁵

Referring to Table 2, for devices fabricated by spin coating fromdichlorobenzene solution and annealed in vacuum at 150° C., DPP-0exhibited the maximum hole mobility of 4.27 cm²·V⁻¹s⁻¹, with an averagemobility of 3.52 cm²·V⁻¹s⁻¹. These results are in line with otherreported DPP-based OFETs. With 30% CBSs along the polymer backbone,DPP-30 surprisingly presented the mobility up to 1.43 cm²·V⁻¹s⁻¹ overthe benchmark value (1 cm²·V^(−l)s⁻¹) for high performance polymers. Therepresentative transfer and output curves of DPP-30 are shown in FIGS.2A and 2B. High hole mobility of up to 4.27 cm²·V^(−l)s⁻¹ in thesaturation regime, well defined on/off current states with on/offcurrent ratio higher than 10⁶ were obtained, indicating good OFETperformance.

With the increasing of CBSs in the polymer backbone, charge carriermotilities of DPP-50, DPP-70 and DPP-100 predictably fell. With over onehundred devices for each polymer measured, it was found that thelogarithmic mobility is nearly proportional to the CBS ratio in aninverse manner, as shown in FIG. 3, which shows the correlation betweenthe mobility and the conjugation break spacer ratio obtained from thestudy on five polymers, namely, DPP-100, DPP-70, DPP-50, DPP-30 andDPP-0.

In conjunction with the solubility improvement, it was demonstrated thatpolymer mobility and solubility could be modulated through theintroduction of CBSs. In other words, a fine balance between performanceand processability can be reached based on needs. The present approachof introducing CBSs into semiconducting polymers will likely play asignificant role in practical applications. Drop-cast devices providedsimilar results, as shown in Table 2. Annealing of the devices at 150°C. in air on a hot plate was also carried out and the results indicatedthat the transistor devices, made from these polymers, namely DPP-100,DPP-70, DPP-50, DPP-30 and DPP-0, have excellent thermal stability inair. The semiconductor layer was deposited on the OTS-treated Si/SiO₂substrates by spin coating and drop casting. For spin coating, spinspeed of 2000 r.p.m. was used to get a good polymer film. Theconcentrations of the solutions used for spin coating were 3 mg/mL forpolymer DPP-0 and 10 mg/mL for the other 4 polymers. The concentrationsof the solutions used for drop casting is ⅓ of those for spin coating.

From DSC studies it was learned that melting transitions exist in DPP-70and DPP-100. Further devices made using DPP-70 and DPP-100 were stablein air from the annealing study. It was hence inferred that thesepolymers will be suitable for the melt processing, a process widelypracticed for making plastic thin films in industry. We fabricated themelt processed OFETs by directly placing DPP-70 and DPP-100 solids onthe pre-patterned, OTS-treated silicon wafer, which was then subjectedto 250° C. and 200° C. in air (with/without nitrogen flow protection),respectively. Performance characteristics of devices usingmelt-processed DPP-70 and DPP-100 are summarized in Table 2. Themotilities are as high as 0.30 and 0.045 cm²·V⁻¹s⁻¹ for DPP-70 andDPP-100, which are two or three times that of the ones processed throughsolution processing. Compared to solution processing methods, meltprocessing completely eliminates the need of using toxic organicsolvents.

To understand the correlation between microstructure and transistorperformance, atomic force microscope (AFM) and grazing incidence X-raydiffraction (GIXRD) studies were performed on both spin-coated andmelt-processed thin films on OTS-covered Si/SiO₂ substrates. The AFMstudy revealed unusual lamellar (layered) microstructures across thespin-coated films for polymers with higher ratio of CBSs (DPP-70 andDPP-100). Each layer was about ˜2.2-2.4 nm thick, which is close to thelamellar spacing for the polymers. In comparison, DPP-0, DPP-30 andDPP-50 exhibit very similar morphologies as often seen in conjugatedpolymers, and no layered packing is present. Layered microstructures areoften found in highly crystalline small molecule thin films but rarelyobserved in semiconducting polymer thin films. This observation suggestsDPP-70 and DPP-100 may resemble small molecules in a way that highcrystallinity is preserved, particularly in their melt processed thinfilms. Increased degree of ordering observed from AFM results iscorroborated by GIXRD studies. All spin-coated polymer thin filmsexhibit a dominant edge-on π-π stacking, favourable for chargetransport.

With the increase of the CBS ratio, the full-width half maximum (FWHM)of both the lamellar and π-π stacking peaks in spin-coated films isreduced by approximately 25% from DPP-0 to DPP-100 as shown in Table 3below:

TABLE 3 Crystallographic Parameters for the spin coated DPP PolymerFilms by GIXRD. DPP-0 DPP-30 DPP-50 DPP-70 DPP-100 lamella spacing 22.2822.07 21.96 21.75 21.64 (Å) lamella peak FWHM 0.044 0.038 0.039 0.0410.035 (1/Å) π-π stacking distance 3.62 3.64 3.65 3.65 3.62 (Å) π-π peakFWHM 0.084 0.078 0.087 0.076 0.063 (1/Å)

The above observation indicates that the crystalline domains become moreordered with the increased fraction of spacers, in line with the AFMobservations. Application of models from literature on the lamellarstacking peaks yields the apparent crystalline domain coherent length of14 nm and 18 nm for DPP-0 and DPP-100, respectively. In addition to thechange in FWHM, the lamellar stacking distance consistently decreasesfrom DPP-0 to DPP-100, albeit slightly, which could be due to closeralkyl chain stacking with increased molecular ordering.

AFM images and GIXRD patterns of DPP-100 by spin-coated andmelt-processed thin films are shown in FIGS. 6A through 6D. A strikingdifference is observed in AFM images. The melt processed film formscondensed layered microstructures, while the spin-coated film exhibitsloosely packed layers. The GIXRD patterns reveal considerably sharperpeaks with a dramatically reduced peak width for the melt-processedfilm, suggesting that much larger domains and/or significantly improvedordering existed in the melt processed thin films. It is worth notingthat such narrow peak widths (0.012˜0.016 A⁻¹) and large apparent domainsizes (40˜50 nm) are not common among polymer materials. A similarobservation is also found in the case of DPP-70. Both AFM and GIXRDresults strongly support that melt processed films have more orderedmicrostructures and packing motifs for charge transport than solutionprocessed films, which is in good agreement with the OFET result thatmelt-processed devices displayed improved charge transportcharacteristics versus solution-processed devices.

Understanding how charge carriers move in the thin film is a criticalstep to design next generation semiconducting polymers. From highmolecular weight tie chain model to disorder-free transport model, thereis much to investigate about charge transport in semiconducting polymerthin films. Our present disclosure provides fresh insights into thesecharge transport models. For instance, DPP-100, having 100% flexibleCBSs along the polymer backbone, obviously lacks intrachain chargetransport pathways. Despite the presence of highly ordered π-stacks, themobility from DPP-100 is about two order magnitude lower than that ofDPP-0. This observation clearly underscores the importance of intrachaincharge transport and a torsion-free polymer backbone as proposed in amodel in the literature. If a small amount of DPP-0 is blended intoDPP-100 to serve as the tie chains, it is possible that there will be adramatic increase in the charge transport of the blended film.

Thus, in this disclosure, the modulation of electronic performance andsolution-processability in semiconducting polymers has been realizedthrough introducing flexible conjugation-break spacers. This approachalso leads to design of high performance melt-processable semiconductingpolymers. Importantly, melt processed thin films present highercrystallinity and more ordered microstructures than theirsolution-processed counterparts, and hence offer substantially improvedcharge transport characteristics. These findings can lead to developmentof low cost melt-processed organic electronics via theindustrially-adapted extrusion and lamination process. Higherperformance melt-processable polymers are possible by those skilled inthe art by extending the approaches described in this disclosure.Fine-tuning the flexible spacer length offers the potential to improvecharge transport. It has been clearly demonstrated that introduction offlexible conjugation-break spacers (CBSs) into semiconducting polymersenables to modulate polymer processability and charge transportproperties, as well as rendering melt-processability to the resultingpolymers with the high CBS loading (≥3 Carbons in a chain, as understoodby those skilled in the art), depending on the length of CBS.

In this disclosure, conjugation-break spacers (CBSs) are intentionallyintroduced into the diketopyrrolopyrrole (DPP)-based polymer backbones.It has been demonstrated in this disclosure demonstrated that thesolution-processability progressively increases with the percentage ofCBSs, while charge mobility inversely varies to the CBS ratio. Forinstance, the polymer DPP-30 with solubility of ˜10 mg/mL indichlorobenzene provides an average mobility over 1.4 cm²·V^(−l)s⁻¹,while DPP-0 exhibits an average mobility of 4.3 cm²·V⁻¹s⁻¹ withsolubility of ˜3 mg/ml. This correlation provides a general guidance todesign polymers with desired electronic performance andsolution-processability for large scale roll-to-roll processing. DPP-70can be melt processed in air and provide hole mobilities up to 0.30cm²·V^(−l)s⁻¹, substantially higher value than their solution-processedcounterparts about 0.1 cm²·V⁻¹s⁻¹. The mobility boost in melt-processeddevices, together with completely eliminating the need to use toxicsolvent in the processing, enables designing melt-processable polymersfor electronic devices.

Based on the above description, we can now describe a semiconductingpolymer composition comprising at least one non-conjugation spacer.Further, the percentage of non-conjugation spacer, measured in mers, canbe varied. In particular, we can have zero percentage (in terms of mers)of non-conjugation spacer and still achieve a semiconducting polymer.Further, it is possible to have a semiconducting polymer which is madeof non-conjugation spacers only.

Based on the above description, a method of making solid-statesemiconducting films using a semiconducting polymer with enhancedsolution processability can be described. The method comprises mixing atleast three monomers in a pre-determined proportion, wherein at leastone of the three monomers contains at least one non-conjugation spacer,to form a mixture. The three monomers in the mixture are then reactedwith one another to achieve polymerization, resulting in a solid statepolymer. The solid state polymer is then purified as known to thoseskilled in the art. The purified solid state polymer is then dissolvedinto an organic solvent to form a homogenous solution. The homogeneoussolution is then deposited onto a substrate. The solvent of the solutionis then evaporated to form a solid-state semiconducting film.

In the above method, non-limiting examples of the three monomers are:3,6-bis(5-bromothiophen-2-yl)-2,5-bis(4-decyltetradecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione;3-bis(5-(trimethylstannyl)thiophen-2-yl)propane; and5,5′-bis(trimethylstannyl)-2,2′-bithiophene. Non-limiting example of thesolvent that can be used in this method are dichlorobenzene,chlorobenzene and toluene.

It is also an aspect of this disclosure to have at least one of thethree monomers, namely(3,6-bis(5-bromothiophen-2-yl)-2,5-bis(4-decyltetradecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione;1,3-bis(5-(trimethylstannyl)thiophen-2-yl)propane; and5,5′-bis(trimethylstannyl)-2,2′-bithiophene) mentioned above contain atleast one non-conjugal spacer. It is advantageous to have these threepresent in the ratio 1:x; (1−x), where x is the number of mers ofmonomer containing the non-conjugation spacer. For the polymerization itis required to have equal amount of reactive functional groups on themonomers to obtain polymers. Otherwise, low molecular weight oligomericspecies will be obtained.

To achieve solid-state semiconducting films from the semiconductingpolymers of this disclosure, several techniques or methods can be usedfor depositing the purified solid-state polymer onto a substrate.Non-limiting examples of deposition methods suitable for this purposeinclude spin-coating, drop-casting, ink-jet printing, and screenprinting.

Many materials can be used as a substrate on which the polymersemiconducting films of this disclosure are deposited. Non-limitingexamples of for the substrate in the methods described above includesilicon wafer, indium-tin oxide, and various types of glass. Manymethods can be used to achieve polymerization. One simple method isheating. One can use a catalyst to aid in the polymerization processduring heating. A non-limiting examples of a catalyst that can be usedfor this purpose is palladium complex.

Based on the above detailed descriptions, we can also describe a methodof making solid state semiconducting films using a semiconductingpolymer with melt processability. In this case, the method comprisesmixing at least three monomers in a pre-determined proportion, whereinat least one of the three monomers contains at least one non-conjugationspacer, to form a mixture, and achieving polymerization of the mixtureby reacting the at least three monomers with one another resulting in asolid state polymer. The solid state polymer is then purified asdescribed by methods known to those skilled in the art, resulting in aquantity of purified solid state polymer. The purified solid statepolymer is then deposited onto a substrate and heated to form a liquidmelt. The liquid melt is then cooled resulting in a solid statesemiconducting thin film.

In the method described above to make a solid state semiconducting filmsusing a semiconducting polymer with melt processability, non-limitingexamples of the at least three monomers are3,6-bis(5-bromothiophen-2-yl)-2,5-bis(4-decyltetradecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione;1,3-bis(5-(trimethylstannyl)thiophen-2-yl)propane;5,5′-bis(trimethylstannyl)-2,2′-bithiophene, wherein1,3-bis(5-(trimethylstannyl)thiophen-2-yl) propane contains at least onenon-conjugal spacer. It is advantageous to have the mers ratio of3,6-bis(5-bromothiophen-2-yl)-2,5-bis(4-decyltetradecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione;1,3-bis(5-(trimethylstannyl)thiophen-2-yl)propane; and5,5′-bis(trimethylstannyl)-2,2′-bithiophene to be 1:x:(1−x) wherein x isthe number of mers of 1,3-bis(5-(trimethylstannyl)thiophen-2-yl)propane.For the polymerization, it is required to have equal amount of reactivefunctional groups on the monomers to obtain polymers. Otherwise, lowmolecular weight oligomeric species will be obtained. Further, in thismethod, it should be noted that many materials can be used a substrateon which the purified silid state polymer is deposited. Non-limitingexamples of such a substrate include silicon wafer, indium-tin oxide,and various types of glass.

While the above description described methods of making semiconductingfilms using at least three monomers, of which at least at least one ofthe three monomers contains at least one non-conjugation spacer, it ispossible to make polymer semiconducting films using at least twomonomers. In the case of using only two monomers, one of them shouldcontain at least one non-conjugation spacer. This case corresponds tox=100 in Scheme 1. In such a case, flexibility of using different typesof polymers is compromised, limiting the approach to alternating typeco-polymers only.

Semiconducting polymers (namely conjugated polymers) are promisingoptoelectronic materials for next-generation flexible and printedelectronics, including organic solar cells (OPVs), organic field-effecttransistors (OFETs), organic light-emitting diodes (OLEDs), andelectrochromic devices, among others. These polymers are typicallyprocessed by organic solvents. At present, however, numerous highperformance conjugated polymers encounter the solubility problem, sothat they have to be processed in chlorinated solvents under hightemperatures. The methods and compositions described in this disclosurecan be used advantageously to develop a new class of polymers thatexhibit much enhanced solution-processability. More importantly, thesecarefully designed polymers enable melt-processing, thus makingfabrication of plastic electronics possible via the extrusion andlamination process for the electronic applications mentioned above andmany other applications.

The foregoing discussion shows that the methods and compositions of thisdisclosure dramatically improve solubility for the polymers, and makesolution-processing possible under ambient conditions and using lesstoxic solvents. Further, the high performance melt-processablesemiconducting polymers described in this disclosure can enable moreenvironmentally-friendly processes and lower costs.

While the present disclosure has been described with reference tocertain embodiments, it will be apparent to those of ordinary skill inthe art that other embodiments and implementations are possible that arewithin the scope of the present disclosure without departing from thespirit and scope of the present disclosure. Thus, the implementationsshould not be limited to the particular limitations described. Otherimplementations may be possible. It is therefore intended that theforegoing detailed description be regarded as illustrative rather thanlimiting. Thus, this disclosure is limited only by the following claims.

The invention claimed is:
 1. A semiconducting polymer compositioncomprising three monomers in a pre-determined proportion, wherein thethree monomers are3,6-bis(5-bromothiophen-2-yl)-2,5-bis(4-decyltetradecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione;1,3-bis(5-(trimethylstannyl)thiophen-2-yl)propane; and5,5′-bis(trimethylstannyl)-2,2′-bithiophene, wherein1,3-bis(5-(trimethylstannyl)thiophen-2-yl)propane contains at least onenon-conjugation spacer.
 2. The composition of claim 1, wherein the3,6-bis(5-bromothiophen-2-yl)-2,5-bis(4-decyltetradecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione;1,3-bis(5-(trimethylstannyl)thiophen-2-yl)propane; and5,5′-bis(trimethylstannyl)-2,2′-bithiophene are in the mer ratio of:1:x:(1-x), wherein x is the number of mers of1,3-bis(5-(trimethylstannyl)thiophen-2-yl)propane.
 3. A semiconductingpolymer composition comprising two monomers in a pre-determinedproportion, wherein the two monomers are3,6-bis(5-bromothiophen-2-yl)-2,5-bis(4-decyltetradecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione,and 1,3-bis(5-(trimethylstannyl)thiophen-2-yl)propane, wherein1,3-bis(5-(trimethylstannyl)thiophen-2-yl)propane contains at least onenon-conjugation spacer.